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High-strength hot-formed steel sheet member

a technology of hot-formed steel and high-strength, which is applied in the direction of heat treatment equipment, manufacturing tools, furnaces, etc., can solve the problems of dimensional precision deterioration, increased springback and wall camber, and difficult production of complex product shapes, etc., and achieves delayed fracture resistance and high strength

Active Publication Date: 2017-04-06
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The invention provides a high strength hot formed steel sheet that can be used as an impact resistant part of an automobile. The sheet has a high tensile strength of 1.7 GPa or more and is stable in hardness and resistant to delayed fracture.

Problems solved by technology

However, along with higher strength, the press formability of steel sheet falls, so production of complicated shapes of products has become difficult.
As a result, for example, along with the higher strength of steel sheet, the problem of the ductility falling and fracture occurring at portions with a high working degree and the problem of the springback and wall camber becoming greater and therefore the dimensional precision deteriorating arise.
Therefore, it has not been easy to press-form steel sheet having a high strength, in particular 780 MPa or more tensile strength, into a product having a complicated shape.

Method used

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  • High-strength hot-formed steel sheet member

Examples

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examples

[0098]Below, examples will be used to more specifically explain the present invention, but the present invention is not limited to these examples.

[0099]Steel having each of the chemical compositions shown in Table 1 was smelted in a test converter and continuously cast by a continuous casting test machine to obtain a width 1000 mm, thickness 250 mm slab. Here, at the conditions shown in Table 2, the heating temperature of the molten steel and amount of casting of molten steel per unit time were adjusted.

[0100]The cooling speed of the slab was controlled by changing the amount of water at the secondary cooling spray zone. Further, the center segregation reduction treatment was performed at the end part of solidification using a roll mill to softly reduce the thickness by a gradient of 1 mm / m and discharge the concentrated molten steel of the final solidified part. In some slabs, after that, a soaking treatment was performed under conditions of 1250° C. and 24 h.

TABLE 1SteelChemical c...

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Abstract

A high-strength hot-formed steel sheet member exhibiting both a consistent hardness and delayed-fracture resistance, and is characterized in that: the high-strength hot-formed steel sheet member has a prescribed chemical composition; the degree of Mn segregation α (=[maximum Mn concentration (mass %) at the sheet center in the thickness direction] / [average Mn concentration (mass %) at a depth of ¼ of the total thickness of the sheet from the surface]) is less than or equal to 1.6; the steel purity value as defined in JIS G 0555 (2003) is less than or equal to 0.08%; the average grain size for prior γ grains is less than or equal to 10 μm; and the number density of the residual carbides is less than or equal to 4×103 particles / mm2.

Description

TECHNICAL FIELD[0001]The present invention relates to a high strength hot formed steel sheet member, more particularly relates to a high strength hot formed steel sheet member excellent in delayed fracture resistance.BACKGROUND ART[0002]In the field of steel sheets for automobile use, to achieve both lighter weight for improved fuel efficiency and improvement of the impact resistance, there has been growing use of high strength steel sheet having a high tensile strength. However, along with higher strength, the press formability of steel sheet falls, so production of complicated shapes of products has become difficult.[0003]As a result, for example, along with the higher strength of steel sheet, the problem of the ductility falling and fracture occurring at portions with a high working degree and the problem of the springback and wall camber becoming greater and therefore the dimensional precision deteriorating arise. Therefore, it has not been easy to press-form steel sheet having ...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C21D9/46C23C2/06B22D11/00C22C38/54C22C38/50C22C38/48C22C38/32C22C38/28C22C38/26C22C38/24C22C38/22C22C38/20C22C38/06C22C38/04C22C38/02C22C38/00C21D8/02C23C2/40C25D3/22
CPCC21D9/46C23C2/40C23C2/06B22D11/001C22C38/54C22C38/50C22C38/48C22C38/32C22C38/28C22C38/26C22C38/24C22C38/22C22C38/20C22C38/06C22C38/04C22C38/02C22C38/002C22C38/001C21D8/0226C21D8/0236C21D8/0263C25D3/22C22C38/00C21D8/021C21D9/48C21D1/673C23C2/02C23C2/12C23C2/024C23C2/0224C21D1/18
Inventor HIKIDA, KAZUOTABATA, SHINICHIROKOJIMA, NOBUSATOMORIKI, TAKAHIRO
Owner NIPPON STEEL CORP
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